Planet Counting? 160 Billion Extra-Solar Planets In The Milky Way, Study Finds

Norman Byrd's picture

A recent study suggests that there are at least 160 billion extra-solar planets, or exoplanets, circling around stars in our galaxy. This is great news for planet hunters and astrobiologists, not to mention all those hoping to find E.T.

Are you a planet hunter? Into counting the number of new worlds being discovered? How about just being interested in whether or not there is alien or extraterrestrial life out there? Well, then, prepare to receive an embarrassment of riches. A recent study conducted by a research team at the Paris Institute of Astrophysics (published in Nature) has found that there won't be a shortage of new worlds to discover and study in the near future. It appears that there might be as many as 160 billion planets within the Milky Way alone.

Using a technique called microlensing, the team, led by Arnaud Cassan, was able to look at six years of data and estimate the number of worlds. By using microlensing, researchers were able to determine whether or not light from faraway stars became bent when passing through the gravitational fields of foreground, or nearer, stars. In this way the scientists could infer that the foreground stars hosted alien planets. Given the number of stars bending light, the team was also able to determine that there were approximately 1.6 planets circling each star in the galaxy. Since there are roughly 100 billion stars in the Milky Way, that would place the number of extrasolar planets at 160 billion.

"This statistical study tells us that planets around stars are the rule, rather than the exception," Cassan said in an email to "From now on, we should see our galaxy populated not only with billions of bright stars, but imagine them surrounded by as many hidden extrasolar worlds."

New planets are being added to the various registries that track exoplanets all the time. Although a majority of the planets discovered thus far are gas giants and hot Jupiters (because their enormous size makes them easier to identify), many of the alien worlds are proving to be just that -- alien. Thus far, researchers have found a world that reflects no light, a planet that is made of nearly pure carbon (a diamond), Super Earths, planets close to their parent stars, planets within the "Goldilocks Zone," planets that circle binary stars, and a few planets roughly the size of Earth.

There might be quite a few more planets in our galaxy than just the 160 billion estimated by Cassan's team. According to another microlensing study released in 2011, the number of planets could be twice as large. The study estimated the number by determining the likelihood of independent "rogue" planets, free-flying worlds that roam the galaxy without being caught in the gravitational field of a parent star.

But will there be life on any of those billions of planets? Astrobiologists -- and quite a number of the world's population -- would like to think so. Perhaps intelligent life as well. The odds seem to weigh heavily in favor of extraterrestrial life -- if it truly exists at all -- being discovered sometime in the future. There certainly won't be a shortage of candidates anytime soon.

(photo credit: Nick Risinger, Wikimedia Commons)


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